Are you using the normal marker or the frequency counter marker? The counter marker should be accurate, while the frequency displayed for the normal marker position will not be. You may be able to improve the normal marker's accuracy in narrow spans if you run the shift-W self-calibration routine but it will never be as good as the counter.
-- john, KE5FX > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Hui Zhang > Sent: Saturday, June 28, 2014 6:49 PM > To: Discussion of precise time and frequency measurement > Subject: [time-nuts] HP 8568B > > Hello all: > Rencently I bought a second-hand HP8568B Spectrum Analyzer, it kind of > vintage but works well. Only problem is its time base lost accurate. When I use > it measured my HP Z3801A output (locked to GPS), the center frequency read is > 9.999912MHz, about 88Hz diffrence. So I decide to use my Z3801A for its > external reference. When I connected the cable and set the reference switch in > rear paneal to EXT, the CRT displayed "EXT REF", I believed it worked. But when > I use it measure a nother GPSDO (Trimble ThunderBolt locked to GPS), it still > have 42Hz diffrence. I am very sure both of my two GPSDO is good, if I use my > HP53132A counter to compare them they will has less 1E-10 (1mHz) diffrence. > And then I tie a BNC three-way connect from my Z3801A, one way to 8568B's > EXT stand input, one way to the signal input in front panel, the diffrence is still > 42Hz - it's 10.000042MHz. I was fully confused, do I need a calibration after I > used external 10Mhz stand? I read the manual again but not fou > nd any infomation about how to do it. What do I do now? Anyone give me a > suggestion? Any infomation will be appreciate. > > > Hui Zhang > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time- > nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
